A Beyer M55 500Ω version was connected directly to a high sensitivity V.T.V.M (vacuum tube voltmeter).
Distance at about 1in, male singing voice as softly and effortlessly as possible.
The Belco VT-250 VTVM was shunted at its input with a resistor of 560Ω.
The average reading was 10 micro volts.
Without the resistor it was 20μV. This is expected since a load of 560Ω shunt to a mic of 500Ω output impedance, by potential decider principle, halves the voltage. This half voltage drop is 6dB as 3dB means doubling of power but doubling the voltage makes the power x4 by the V squared over R power relation.
By inserting a Pleiades V(-1) prepreamplifier between the mic and the terminated VTVM to voltage reading for same singing effort was 100μV or 0.1mV.
This may be a significant difference considering that almost no extra noise or hiss is added what already exists at the mic output.
Is this about 20dbm voltage gain or about 10dB power gain?
References:
Electronics, a systems approach - Neil Storey
https://en.m.wikipedia.org/wiki/Gain_(electronics)
http://www.sengpielaudio.com/calculator-gainloss.htm
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